I think you are right about the multiarch-support functions being native in bullseye. I had the following additional source added to my /etc/apt/sources.list form earlier experiments, and I'm guessing this is where the package is located:
deb http://ftp.de.debian.org/debian buster main contrib non-free
I think that contrib and non-free are not necessary to locate the package. This should be added to the end of the sources.list in addition to the bullseye sources.
Based on elilla's comment, it might be easily playable on a virtual machine. Hopefully, it runs on buster with minimal effort in the virtual environment. Would your computer handle a virtual machine?
Edit 1: I tried it in a virtual machine and it worked fine. My installation of bullseye was new and did not have wine, after installing it the game works under bullseye without virtualization.
Edit 2: The package can be obtained directly from Debian's repository and installed with
wget http://ftp.us.debian.org/debian/pool/main/g/glibc/multiarch-support_2.28-10+deb10u1_amd64.deb sudo dpkg -i multiarch-support_2.28-10+deb10u1_amd64.deb